Varjas said he sold secretly motorised bicycles to an unknown client just before the 2015 Tour, delivering the bikes to a locked storage room.

The silent motor, which is made of military-grade metal, is powered by a lithium battery. A secret button provides a power boost for 20 minutes.

ACTIVATE

The motor can also be activated when a rider's heart rate gets too high, by linking it remotely with the rider's heart-rate monitor, said Vargas.

He noted one motor design can be hidden inside the hub of the back wheel but would boost the normal wheel weight by about 800 grams.

In the 2015 Tour de France, peloton bikes were weighed before a time-trial stage, with CBS reporting French authorities said Team Sky were the only squad with heavier bikes, each about 800 grams more.

Britain's Chris Froome, riding for Sky, won the 2013, 2015 and 2016 Tour de France crowns.

In 2015, he was also "King of the Mountains" for his times in the tough climbing stages that often prove decisive.

A Team Sky spokesman told CBS the team never used mechanical assistance, saying time-trial bikes might be heavier to allow for better aerodynamics and all Sky bikes were cleared by the International Cycling Union. - AFP